The present invention relates generally to a system for protecting a drill string from ice movement in ice covered waters.
Geologists presently feel that off-shore regions in the Arctic show great promise for the exploration and production of oil and gas. This expectation is bolstered by major gas and oil finds recently made on land in the vicinity of the MacKenzie Delta and Prudhoe Bay, and by the fact that off-shore areas are usually more productive than adjacent land areas. When off-shore drilling operations are conducted in a temperate zone, conventional shallow water drilling methods and production platforms may be employed. However, in view of the extreme cold and harsh conditions which exist north of the Arctic Circle, the drilling and maintenance of off-shore wells in the Arctic has been extremely difficult. Particularly since the Arctic Ocean is covered with an ice sheet for a good portion of the year. The ice sheet may typically be five to six feet in depth, and and eight to ten foot sheet is not uncommon. Further, the Arctic ice sheet is characterized by extreme irregularities resulting from deformations thereof. One form of ice sheet irregularity is called a pressure ridge, which is normally a long narrow section of ice which has been built up to be many times thicker than the thickness of the surrounding ice sheet. Pressure ridges sometimes extend fifteen feet or more above the surface of the ice sheet and fifty feet or more below the surface. The movement of the ice sheet depends upon its location in the Arctic. At some locations the ice sheet moves only slightly, while at others movements of up to one mile per day, at a rate of up to five miles per hour, are not uncommon. Under these conditions, the present invention was conceived to support a drill string in the Arctic, while protecting it from damage caused by movement of the ice.